1. Field of the Invention
The invention relates to a gas-transmitting wall element for a metallurgical vessel lined with refractory material. In this specification and in the context of the invention, the term metallurgical vessel includes a converter for steel-making as well as steel ladles and treatment vessels for non-ferrous metals. The gas-transmitting wall element is suitable for fitting either into the bottom wall or into the side wall of the vessel. The invention also relates to a metallurgical vessel including such a wall element, and to a method of steel making by the "LD-process".
The invention will be described here in particular with reference to the application of the gas-transmitting wall element in a steel converter, but the invention is expressly not restricted to this application.
2. Description of the Prior Art
When making steel in a steel converter, a tilting vessel is often used, in which oxygen is blown at the top of the vessel onto the molten iron in the vessel. This may or may not be accompanied by the charging of scrap and/or slag-forming additives.
At present there is a great deal of interest in processes in which gas is also blown in at the bottom. To do this, for example, a very porous bottom brick is used to inject non-oxidising gases such as argon, nitrogen or CO. The purpose of this is to produce extra mixing in the metal bath, and by means of this scavenging gas to remove unwanted elements from the bath.
Processes have also been proposed in which blast pipes or blast pipes with a ring gap are used. In this case, within a flow of non-oxidixing buffer gas, other gases such as oxygen, CO.sub.2, argon, nitrogen or air can be blown in. There are also proposals completely to replace the oxygen supply from above by oxygen which is blown in from below through the bottom.
One drawback of the known structures with inlet pipes, whether or not these are combined with a ring gap, is the need to blow in a substantial quantity of gas during the whole time that a bath is present in the vessel. This is to prevent fluid from the bath leaking into the pipes and/or ring gap. In addition it has been found that these pipes can be susceptible to very rapid wear at the rate of a few mm per charge. Also, when using pipes, solidification of the steel may occur because of excessive local cooling at the pipe or close to it; this can prevent the required continuous flow of the gaseous element.
High cost is a drawback of the use of porous bricks. This is a result of the complicated way in which these bricks are produced, in that during moulding of the brick a large number of pores or channels of a very small diameter have to be produced which have to remain intact while the brick is being fired. It has been found that the reproducibility of the porosity is poor and also that the range over which the porosity can be varied is small.
DE-A-No. 2719829 discloses a gas-transmitting wall element having a refractory brick whose side and base walls are narrowly spaced from a metal housing. Near the base there are grooves in the brick. It is difficult to maintain this narrow spacing in practice, because of the pressures on the wall element and the problem of locating the brick accurately in the housing.